This application addresses broad Challenge Area 04, Clinical Research and specific Challenge Topic 04-AI-102 - The human immune response to infection and immunization - Profiling via modern immunologic methods and systems biology. The development and maintenance of memory T cells is a hallmark of the host response to acute and persistent viral infections and a major objective of vaccination for infectious diseases and cancer. Analysis of the phenotype and function of memory T cells in both mice and humans has identified two broad subsets of long-lived memory cells termed central memory (TCM), defined by expression of CD45O and CD62L;and effector memory (TEM), defined by expression of CD45RO and the absence of CD62L. Recent work in the applicant's lab has identified a subset of quiescent memory CD8+ T cells in normal individuals that express cell surface markers that enable their separation from the more prevalent TCM and TEM subsets, and includes molecules shared by hematopoietic stem cells. These quiescent memory T cells exhibit higher ATP binding cassette (ABC) transporter activity, rapidly efflux fluorescent dyes and chemotherapy drugs and are resistant to cytotoxic chemotherapy in vitro and in vivo compared with the majority of memory T cells. The high-effluxing T cells have a diverse T cell receptor repertoire, contain T cells specific for persistent and acute viruses, and contribute to repopulation of memory T cells in individuals who have received chemotherapy. Preliminary gene expression arrays performed on sort-purified subpopulations of memory and na[unreadable]ve T cells demonstrate that the subsets of memory T cells with high efflux capacity have a distinct transcriptional profile compared with the majority of TM cells, and with TN cells. The studies in this challenge grant will deliver a detailed database on the frequency, functional properties and gene expression profile of these novel subsets of human antigen experienced T cells, and elucidate their development after vaccination. The potential impact of this work relates to improving our understanding of the mechanisms responsible for the durability of human CD8+ T memory in normal individuals and those undergoing chemotherapy or vaccination. The studies have implications for elucidating the nature of protective immunity that might be elicited by vaccines for infectious diseases and cancer, and could provide a marker for the integrity of host immunity to pathogens in aging. The specific aims are: Aim 1. To compare the frequency, transcriptional profile and factors governing maintenance and differentiation of chemotherapy resistant IL-18R?hi CD161hi subsets of human memory CD8+ T cells with IL-18Rlo CD161lo subsets of TCM and TEM, and with TN. The proposed studies will determine the frequency of CMhi and EMhi in normal adult humans (age 18-80), determine the transcriptional profile of these subsets in ten donors, and compare the functional properties of CMhi and EMhi with the respective non-effluxing subsets and with TN. Aim 2. To determine if primary or booster vaccination of humans with vaccinia virus induces a longlived subset of vaccinia virus-specific CD8+ CMhi and EMhi T cells. The time after infection or vaccination when this novel subset of IL18R?hi CD161hi virus-specific T cells might develop has not been defined. The proposed studies will examine the presence of vaccinia virus specific T cells in individuals with remote vaccinia immunization, recent vaccinia boosting and in vaccinia na[unreadable]ve individuals receiving a primary vaccination. PUBLIC HEALTH RELEVANCE: The development and maintenance of memory T cells is a hallmark of the host response to acute and persistent viral infections and a major objective of vaccination for infectious diseases and cancer. Progress in defining the qualitative attributes of memory T cells that contribute to their longevity has been much less significant, particularly in humans. Addressing these issues requires a greater understanding of the subsets of T cells that make up the human memory T cell pool and the application of novel approaches to interrogate the cellular and molecular programs that maintain these cells. The studies in this challenge grant will determine the frequency, functional properties and gene expression profile of novel subsets of human memory T cells that have characteristics of long-lived cells, and elucidate their development after vaccination. The potential impact of this work relates to improving our understanding of the mechanisms responsible for the durability of human CD8+ T memory in normal individuals and those undergoing chemotherapy or vaccination.